This invention relates to methods and apparatus for producing coherent or monolithic elements, such as rods of amorphous or monocrystalline material, and, more particularly, to methods of growing such elements which are characterized by high purity and freedom from dislocations and discontinuities.
The most important present commercial utilization of the present invention is in the production of semi-conductor materials, such as are extensively utilized in the electronics industry, but it is to be understood at the outset that the present invention may be utilized for the production of other than semi-conductor crystals or materials, such as crystalline materials in the nature of rubies for laser applications, grainless metals, amorphous materials, and the like. For purposes of illustrating the present invention, however, the material produced will be assumed to be monocrystalline semi-conductor materials having uniform physical and chemical properties.
The production of crystals having exceedingly high purity or freedom from dislocations has become increasingly important, especially for the production of semi-conductor materials for use in the electronics industry as well as for use in basic research.
Monocrystalline materials, e.g., semi-conductor materials, comprising, e.g., silicon or germanium have previously been produced by several basic methods. All of the previously suggested techniques have been based upon variations of two basic crystal growth mechanisms. One such mechanism is the Czochralski technique and the other is that of zone melting. The Czochralski technique, and the various variations thereof, produce monocrystalline structures by pulling a single crystal from a molten mass of raw material contained within a crucible. Zone melting techniques do not use a crucible, but rather melt only a very small region of a polycrystalline bar, as by radio-frequency induction, and depend upon surface tension of the molten zone to retain the molten material relative to the crystalline material.
The crucibles utilized in the Czochralski growth techniques are generally fabricated of a relatively inert material, such as quartz. The presence of even an inert material such as quartz in contact with the molten material invariably produces some oxygen contamination of the melt at the relatively high temperatures necessary. The zone melting techniques, on the other hand, depend upon surface tension of the molten zone to retain the molten material in position and generally produce excessive crystal dislocations, strains or discontinuities because of the large temperature differentials inherently present in such a thin molten zone.
Accordingly, it is a primary object of the present invention to produce monolithic structures or elements which are of high purity, coherent, and dislocation or discontinuity-free, and possessing uniform physical, chemical and electrical properties.
Another primary object of the present invention, in addition to the foregoing object, is to produce high purity monocrystalline structures which are relatively dislocation-free.
Another primary object of the present invention, in addition to the foregoing objects, is to produce monocrystalline structures of high purity.
Another primary object of the present invention, in addition to each of the foregoing objects, is to produce such structures of larger diameter than heretofore capable of production.
Another primary object of the present invention, in addition to each of the foregoing objects, is to produce such structures by controlled accretion from a molten mass.
Yet another primary object of the present invention, in addition to the foregoing objects, is to provide methods and apparatus for producing such structures continuously, rather than by batch techniques.
A still further primary object of the present invention, in addition to the foregoing objects, is to provide methods and apparatus for producing such structures which enable finely controlled doping thereof to be easily and readily accomplished.
A still further primary object of the present invention, in addition to each of the foregoing objects, is to provide such methods and apparatus producing a generally uniform physical and chemical property profile across the growing structure-melt interface.
Another and yet still further primary object of the present invention, in addition to the foregoing objects, is to provide such methods and apparatus which enable relatively uniform relative movement between the growing structure and the melt.
Another and yet still further primary object of the present invention, in addition to the foregoing objects, is to provide such methods and apparatus which precludes contamination of the structure material.
It is also a primary object of the present invention, in addition to the foregoing objects, to provide such methods and apparatus having a minimum complexity and a maximum ease of operation.
It is a feature of the present invention that the structure production may be terminated at any desired time and the melt allowed to solidify, without damage or loss of materials.
The invention resides in the combination, construction, arrangement and disposition of the various component parts and elements incorporated in improved methods and apparatus for element growing in accordance with the principles of this invention. The present invention will be better understood and objects and important features other than those specifically enumerated above will become apparent when consideration is given to the following details and description, which when taken in conjunction with the annexed drawing describes, discloses, illustrates and shows certain preferred embodiments or modifications of the present invention and what is presently considered and believed to be the best mode of practicing the principles thereof. Other embodiments or modifications may be suggested to those having the benefit of the teaching herein, and such other embodiments or modifications are intended to be reserved especially as they fall within the scope and spirit of the subjoined claim.